JP2556057B2 - Color image recording method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method of recording a color image using an electrostatic latent image.

2. Description of the Related Art Conventionally, various kinds of color recording methods utilizing electrophotography have been known, and one of them is a superposition developing method. Overlapping development method is a binary or three
The first latent image of the photoconductor having the latent image of the value is developed by the first developing machine, and then the second latent image on the photoconductor is developed by the second developing machine to finally form the final latent image. The toner image is transferred at one time to obtain a color image.
This is effective because the copying speed is extremely fast with the miniaturization of the device.

In such an overlapping developing method, after the second developing step, the photosensitive member bearing the toner image is already rubbed by the developer again in the first developing step. The toner image formed by the developing process is
The toner image is significantly disturbed by the second and subsequent development steps, the second toner is newly developed on the toner image to cause color mixing, and the disturbed toner is mixed in the developing device and the second developer Trouble occurs such as shortening the life. And
If the image density of the toner image formed in the first developing step is increased, the toner image is likely to be disturbed in the second developing step, and the range of conditions for satisfying both the problems of the image density and the disturbance of the toner image. There is a problem that is narrow.

As a method for developing without disturbing the toner image on the photoconductor, (1) non-contact developing method in the latter developing step (Japanese Patent Laid-Open No.
(144452 gazette), (2) It is possible to use a magnetic brush developing method in which the rubbing force is weakened (JP-A-55-36889, JP-A-57-79970 and JP-A-60-126665).

Problems to be Solved by the Invention In the above method (1), for example, JP-A-56-1444 is used.
As disclosed in Japanese Patent No. 52, when the non-contact AC flying method is adopted in the second developing step, considering the flying development by the AC electric field of the toner already developed, the disturbance of the first toner image, the second developing It is not a good idea in terms of the mixture of the agent into the first toner image.

In the method (2), since the developing efficiency or the developing ability in the second developing step is lowered,
There is a problem that it is difficult to develop with a sufficient image density.

The present invention has been made in view of the above problems in the conventional technique.

An object of the present invention is that the toner image formed in the first developing step is not disturbed even in the second developing step, so that a color image having sufficient image density without color mixing and image disturbance can be obtained. It is to provide a color image recording method.

The present inventors have previously proposed a method of developing using a plurality of developing rolls in the first developing step (Japanese Patent Application No. 62-88629). According to this method, the above problems can be solved to some extent, but as a result of further study, when the charge amount of the toner image formed in the first developing step is high, as shown in FIG. It was found that the image is less likely to be disturbed even in the second developing step. FIG. 3 shows the relationship between the charge amount of the toner image formed in the first developing step and the disturbance of the toner image due to the second developing step. The vertical axis shows the disturbance of the toner image (according to the first developing step). The ratio of the width of the line image by the first developing step after the second developing step to the width of the line image) is shown in the horizontal axis. In case of μc / g and −9.7 μc / g, in the figure, ○
Indicates a toner image formed by the first developing step, and ● indicates the toner image after the second developing step. As is clear from FIG. 3, when the charge amount of the toner image in the first developing step is high, the disturbance of the toner image in the second developing step is small.

Means for Solving the Problems The inventors of the present invention have conducted investigations focusing on this fact, and as a result, in order to increase the charge amount of the toner image formed in the first developing step, a plurality of developing rolls are used. It has been found that development may be carried out under different conditions shown below, respectively, and the present invention has been completed.

The present invention comprises a latent image forming step of forming an electrostatic latent image on a latent image carrier by a latent image forming means, and a developing step of visualizing the formed electrostatic latent image with toners of two or more colors. When,
A transfer step, and after repeating at least the developing step of the latent image forming step and the developing step a plurality of times,
In a color image recording method for transferring a visualized color toner image onto a transfer material, two developing rolls are used in the first developing step among a plurality of developing steps.
It is characterized in that the developing rolls are arranged so that the nip density of the first developing roll of the individual developing rolls becomes smaller than the nip density of the second developing roll.

In the present specification, the “nip density” means that the layer thickness of the toner conveyed on the developing roll is m (mm) and the distance between the developing roll and the latent image carrier is g (mm). It means the value of m / g. FIG. 2 is an explanatory diagram for explaining the nip density, and a layer regulating member is provided on the developing roll 31.
A toner layer having a layer thickness m is formed by 33, and the toner layer is conveyed to a nip region having a gap g formed between the toner layer and the photosensitive layer 10a which is a latent image carrier.

In the present invention, of the plurality of developing rolls in the first developing step, the nip density in the first developing roll is
Each developing roll is arranged so as to be smaller than the nip density in the second developing roll, but preferably, the nip density in the first developing roll is 0.6 to 0.8,
The second developing roll is arranged so that the nip density is 1.0 to 1.5. Further, in that case, it is desirable that the gap g between the developing roll and the latent image carrier is set within the range of 0.6 to 1.2 mm for both the first developing roll and the second and subsequent developing rolls.

In the present invention, the adjustment of the nip density so that the nip density of the first developing roll is smaller than the nip density of the second developing roll adjusts the layer thickness of the toner layer by the layer regulating member. In particular, it may be performed, or by adjusting the distance between the latent image carrier and the developing roller. That is, for example, the gap between the first developing roll and the second developing roll with respect to the latent image carrier may be made constant, and the gap between the layer regulating member in each developing roll may be changed. The developing roll and the second developing roll may have a constant gap between the layer regulating member and the gap between the developing roll and the latent image carrier. Moreover, you may combine them.

Hereinafter, the color image recording method of the present invention will be described with reference to the drawings.

FIG. 1 is an example of a color recording apparatus used for carrying out the present invention and shows a case where a color image is formed by forming a binary latent image. In FIG. 1, 1 is a charger, 2a is a first exposing means, 3a is a first developing means, 2b is a second exposing means, 3b is a second developing means, 4 is a transfer corotron, 5 is a discharging corotron, and 6 is Cleaner, 7 static eliminator, 8 recording paper, 9 pre-transfer corotron, 10 photoconductor drum, 31
And 32 are developing rolls.

The photoconductor drum 10 is rotating in the direction of the arrow. First, the photosensitive layer 10 on the surface of the photosensitive drum 10 is charged by the charger 1.
a is uniformly charged.

Next, light irradiation is performed by the first exposure unit 2a in accordance with the image information corresponding to the first color, and an electrostatic latent image corresponding to the first color is formed on the photoconductor. Any exposure means can be selected. Then, by the first developing means 3a, the toner corresponding to the first color is supplied to the photosensitive layer 10a having the first electrostatic latent image formed by the first exposing means,
Make it visible. There are two developing rolls 31 and 32 in the first developing means.

In the present invention, among these two developing rolls,
It is necessary to arrange each developing roll so that the nip density in the first developing roll is smaller than the nip density in the second developing roll. As these developing rolls, for example, a developing sleeve and an 8-pole symmetric magnet roll are used.

Subsequently, the second exposure unit 2b irradiates light according to the image information corresponding to the second color, and an electrostatic latent image corresponding to the second color is formed on the photosensitive layer 10a. The exposure means and the writing method are arbitrary. Then, the second developing means 3b is formed on the photosensitive layer 10a having the second electrostatic latent image formed by the second exposing means.
Thus, the toner corresponding to the second color is supplied to visualize the toner.

The pre-transfer corotron 9 is used to align the polarities of the first toner and the second toner carried on the photoconductor before transfer, but this can also be omitted in the specific process. The first toner image and the second toner image are transferred onto the recording paper 8 by the transfer corotron 4, but they may be transferred using a means other than electrostatic transfer. The recording paper is then fixed by a fixing unit (not shown). Also, when the photoconductor passes through the transfer section,
Cleaning is performed by the static elimination corotron 5, the cleaner 6 and the optical static eliminator 7 for reuse.

The first and second exposing means include a light illuminating means, a document scanning means and an optical system as used in a normal copying machine, an optical writing device capable of optical modulation according to image information, for example, a laser. Any device such as a writing device, a liquid crystal light valve consisting of a uniform light source and a liquid crystal micro shutter, an LED array, and an optical fiber can be used according to the purpose. In some cases, a second charging unit may be provided before the second exposure unit.

Effect According to the present invention, in the first developing step, among the toner images formed by the development by the first developing roll, the one having a low charge amount is scavenged during the development by the second developing roll. (Cleaned) and as a result
The toner image formed by the second developing roll has a high charge amount and is in a densely packed state. Therefore, in the second developing process, when developing with the toner corresponding to the second color, the toner image corresponding to the first color formed in the first developing process is not disturbed, and the second color is formed with high density. A corresponding toner image is formed.

Examples Hereinafter, the present invention will be described with reference to Examples.

A copy test was conducted using the color image recording apparatus as shown in FIG.

A selenium-based drum having an outer diameter of 200 mm was used as the photosensitive drum, and was uniformly charged to 1000 V by the first charger.
Next, reverse exposure is performed using the LED array, and the exposure unit 200
An electrostatic latent image having a surface potential of V and a non-exposed portion of 1000 V was formed. This electrostatic latent image was developed with a positively charged black developer under a developing bias of 800 V by the first developing means. Then, it was uniformly charged to 1000 V by the second charger. Further, reverse exposure is performed by the LED array to form an electrostatic latent image having the surface potential of the non-exposed portion 1000V and the exposed portion 200V.
Development was performed using a positively charged red developer under a developing bias of 600 V by a developing means. The operating conditions in this case were as follows.

The moving speed of the photosensitive drum was set to 50 mm / sec. As the developing rolls, in the first developing means, two rolls composed of a stainless steel sleeve having an outer diameter of 40 mm and an 8-pole symmetric magnetizing roll having an outer diameter of 20 mm were used. In each of the two developing rolls, the distance m from the layer regulating member was set to 0.9 mm. The first developing roll was arranged so that the gap g between the developing roll and the photosensitive layer was 1.0 mm, and the second developing roll was arranged so that g was 0.6 mm. The positively charged black developer used in the first developing means is a two-component developer composed of black toner and ferrite carrier particles having a particle diameter of 80 μm in both the first developing roll and the second developing roll. Met.

Further, in the second developing means, a stainless steel sleeve having an outer diameter of 40 mm and an 8-pole symmetrical magnetizing roll having an outer diameter of 20 mm are used.
A developing roll was used that creates a repulsive magnetic field in the developing nip area. The positively charged red developer used in the second developing means is a two-component developer composed of red toner and carrier particles having a density of 2.2 g / cm ³ and magnetic particles dispersed in a binder resin and a particle size of 40 μm. It was

When the operation was performed under the above conditions, no mixed color or image disorder of the toner image occurred even at 20 kc / V. Also, the density of the toner image in the second development was sufficiently high.

In the above case, when the charge amount of the toner image formed in the first developing step was examined, the charge amount was 15.4 μc /
It was g.

Comparative Example When the same operation as in Example was carried out except that the second developing roll was omitted in the first developing means in the above examples, color mixing of the toner image occurred at about 5 kc / V.

In this case, the charge amount of the toner image formed in the first developing step was 0.84 μc / g.

EFFECTS OF THE INVENTION The present invention, as described above, includes
Two developing rolls are used in the first developing step, and the nip density of the first developing roll of the two developing rolls is smaller than that of the second developing roll. Since each developing roll is arranged to perform development, the toner image formed in the first developing step has a high charge amount and a sufficient image density, and therefore is not disturbed in the second developing step.
Therefore, according to the present invention, there is no color mixture and image distortion,
A color image having sufficient image density can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color image recording apparatus used for carrying out the present invention, FIG. 2 is an explanatory diagram for explaining the nip density, and FIG. 3 is a toner image formed in the first developing step. 6 is a graph for explaining the disturbance due to the second developing step of FIG. 1 ... Charger, 2a ... First exposure means, 2b ... Second exposure means, 3a ... First developing means 1, 3b ... Second developing means, 4 ...
... Transfer corotron, 8 ... Recording paper, 10 ... Photosensitive drum, 10a ... Photosensitive layer, 31 and 32 ... Developing roll, 33 ... Layer regulating member.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Adachi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Innovator Nobuma Furuya 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Business In-house

Claims (2)

(57) [Claims] 1. A latent image forming step of forming an electrostatic latent image on a latent image carrier by a latent image forming means, and a developing step of visualizing the formed electrostatic latent image with two or more different toners. Process and
A transfer step, and after repeating at least the developing step of the latent image forming step and the developing step a plurality of times,
In a color image recording method for transferring a visualized color toner image onto a transfer material, two developing rolls are used in the first developing step among a plurality of developing steps.
A color image recording method characterized in that the developing rolls are arranged such that the nip density of the first developing roll of the individual developing rolls becomes smaller than the nip density of the second developing roll, and the development is performed. . 2. The nip density of the first developing roll is 0.
6 to 0.8, and the nip density of the second developing roll is 1.
The color image recording method according to claim 1, wherein the color image recording method is 0 to 1.5.